Method and device for the determination of the gas permeability of a container

ABSTRACT

The invention relates to a method and device for the determination of the gas permeability of a container, for example, a PET bottle. Said container is enclosed by a sheath, which hermetically seals the container from the environment. The intermediate space, between the container and the sheath, has only a very small volume in comparison to the volume of the container. The determination of the gas permeability is begun by bringing said intermediate space to, for example, atmospheric pressure, whilst the container is filled with a test gas by means of a special feed, until the container is at an overpressure relative to the intermediate space. The pressure in the intermediate space increases by means of the resulting diffusion of the test gas through the wall of the container into said intermediate space. The increase in pressure per unit time is a measure of the permeability of the container.

This application is a 371 of PCT/EP00/13139 filed Dec. 22, 2000.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a device and a method for determining the gaspermeability of a container.

Nearly all fixedly closed containers have a greater or lesserpermeability with respect to gases. In particular synthetic materialbottles, for example, comprised of polyethylene terephthalate (PET) tendto release gases, for example CO₂, to the outside if their internalpressure is greater than the external pressure. The intention istherefore to decrease the gas permeation through a coating on the insideand/or on the outside of these bottles.

In order to be able to detect the improvements attained through suchcoatings, it is necessary to define the gas permeability of the bottlesbefore and after the coating. To this end, measuring instruments arerequired for determining the gas permeability or the permeation.

In order to inspect the tightness of a container, it is already known togenerate with the aid of excess pressure in the container the diffusionof gases to the outside (Prospectus of Leybold-Heraeus GmbH,“Industrielle Dichtheitsprüfung”, 1987, pp. 64, 65). In this excesspressure method the test sample is filled with a test gas or a mixtureof test gas and air and provided with an encompassing enclosure of knownvolume. The test gas leaking out through the leaks of the test sample isconcentrated in the enclosure and is measured with a sniffing probeafter a defined concentration or service life.

Of disadvantage herein is that a complicated and expensive sniffingprobe is applied, which includes a mass spectrometer (cf. Wutz, Adam,Walcher, Theorie und Praxis der Vakuumtechnik, Fourth Edition, 1988, pp.466, 467). With every change of the test gas, the mass spectrometer mustalso be replaced every time or must be newly calibrated.

Furthermore, a method for measuring the gas permeability of the walland/or of the closure of three-dimensional enclosure bodies is known, inwhich the enclosure body to be tested, which contains a gaseous fillingat atmospheric pressure, is placed into a measuring chamber and the freespace between the enclosure body and the inner measuring chamber isloaded up with filling bodies (DE 26 10 800). Subsequently, anunderpressure is generated in the measuring chamber and the time ismeasured within which a certain pressure rate of ascent interval is runthrough, and the time required for this represents a measure of theleakage rate of the enclosure body and/or of the closure. The pressuremeasurement is performed with a Pirani vacuum gauge, which is aresistance manometer whose electric resistance is a function of the gaspressure. Of disadvantage in this Pirani or heat conduction measuringelement is that it operates accurately only in a pressure range from0.01 mbar to 1 mbar and inaccurately in the pressure range from 10 to1000 mbar and has only minimal resolution for pressures greater than 100mbar. In this method is additionally of disadvantage that in themeasuring chamber an underpressure up to 0.02 Torr (=0.027 mbar=2.7 Pa)must be generated. For this purpose a vacuum pump is required.

It is furthermore known in leak detection technology to detect a leak ina test sample through an excess pressure in the test sample (Wutz, Adam,Walcher: Theorie und Praxis der Vakuumtechnik, Fourth Edition, 1988, p.483). Herein the test sample with volume V is filled via a valve withtest gas until the desired pressure p₁ is reached. The valve issubsequently closed and the time interval Δt is measured within whichthe pressure decreases by Δp₁<<p₁. The total leakage rate of the testsample is in this case$q_{L} = {V \cdot {\frac{\Delta\quad p_{1}}{\Delta\quad t}.}}$

The detection sensitivity in excess pressure leak detection by measuringthe pressure decrease is limited to 1 mbar·l·s⁻¹. However, this valuecan only be reached when using special difference pressure measuringinstruments. Thus, in the case of this leak detection technology, anunderpressure is not generated outside of the test sample but rather anexcess pressure in the test sample. Since no limited and defined volumeexists outside of the test sample, a pressure drop must be measured inthe test sample itself. Herein is disadvantageous that with test sampleswith large volume it takes a long time until there is an onset of alinear pressure decrease.

The invention is based on the task of ascertaining with simple andcost-effective measuring instruments the permeation of containers, inparticular of synthetic material containers.

This task is solved according to the present invention.

The invention consequently relates to a device and a method for thedetermination of the gas permeability of a container, for example of abottle comprising PET. This container is therein encompassed by anenclosure which hermetically seals the container against theenvironment. The interspace between the container and the enclosure hasa very small volume in comparison to the volume of the container. At thebeginning of the determination of the gas permeability this interspaceis brought to, for example, atmospheric pressure while into thecontainer is supplied test gas via special inlet lines until thiscontainer is at an excess pressure in comparison to the interspace.Through the subsequent diffusion of the test gas through the wall of thecontainer into the interspace, the pressure in the interspace increases.The pressure increase per unit time is a measure of the gas permeabilityof the container.

The advantage obtained with the invention comprises in particular thatby employing simple pressure measuring instruments the permeation in thecontainer can be ascertained independently of the gas selected in eachinstance as the excess pressure medium. The ascertainment of thepermeation, in addition, is carried out relatively fast. Added to thisis the fact that improvement of the gas impermeability by coating thecontainer, for example by means of PVD, CVD, or PECVD methods can bedetected very quickly. This is in particular of significance in the caseof beverage bottles filled with CO₂-containing liquids. Without coatingsuch bottles lose approximately 3% of their carbon dioxide per week. Itis furthermore of advantage that the invention is not restricted to aspecific test gas. Apart from CO₂, oxygen, helium or mixtures of gasescan therefore also be utilized.

An embodiment example of the invention is depicted in the drawings andwill be explained in the following in further detail.

FIG. 1 shows a device for the ascertainment of the permeation of asynthetic material bottle without depiction of a pressure sensor.

FIG. 2 shows a curve representing the pressure increase in a containerencompassing a synthetic material bottle.

FIG. 3 shows a configuration with several devices for the ascertainmentof the permeation of different synthetic material bottles.

FIG. 4 shows a configuration of four devices for the ascertainment ofpermeation of synthetic material bottles, with the containerencompassing the synthetic material bottles being removed from onedevice.

FIG. 5 is a representation in principle which shows the securement of acontainer, which is slipped over a synthetic material bottle.

FIG. 6 shows a configuration as in FIG. 4, however, with two furtherconfigurations covered with hoods.

FIG. 7 shows a complete installation with a total of threeconfigurations, each of which comprises four devices for measuring thepermeation of synthetic material bottles.

DETAILED DESCRIPTION

In FIG. 1 a bottle 1 comprised of synthetic material is depictedstanding upside down, which has a known volume V₁. Instead of a bottle,any other hollow body could be employed. The bottle 1 is encompassed bya pressure-tight and hermetically sealed container 2 with known volumeV₂, the interspace 3 between the container 2 and the bottle 1 thus hasthe volume V₃=V₂−V₁. For the ratio of volumes of bottle 1 and container2 applies V₂−V₁<V₁, i.e. the volume of the interspace 3 is less than thevolume of bottle 1. At the start of the permeation measurement incontainer 2, and thus also in the interspace 3, preferably atmosphericpressure p₀ obtains. In contrast, in bottle 1 an excess pressure isobtained and is caused by a specific gas, for example by CO₂, whichpreviously is introduced into bottle 1. Bottle 1 comprises at the end ofits neck a screw threading 4 which engages a closure cap 5. Before thisclosure cap 5 is screwed onto bottle 1, into this bottle 1 a pressuregas is introduced, for example CO₂ in the form of dry ice. The closure 5is introduced into an opening 6 of a closure cover 7 in order to closecontainer 2. This opening 6, in turn, is closed with a cap plug 8, whichcomprises a cover 9. Between the closure cover 7 and a flange 10 ofcontainer 2 is provided a sealing ring 11. Similarly, between cover 9and the cap plug 8 a sealing ring 12 is disposed. In the upper region ofcontainer 2 is provided a connecting piece 13, in which can be disposeda pressure sensor. The flange 10 is a clamping flange welded to thecontainer 2, while the cover 9 is a blanked-off seal plate which closesoff the cap plug 8 by mean of sealing ring 12.

If in bottle 1 according to definition a CO₂ pressure p_(F1) obtains andin the interspace 3 an air pressure p_(Z), where p_(Z) initiallycorresponds to the atmospheric pressure p₀, and if, in addition,p_(F1)>p_(Z), through the excess pressure obtaining in bottle 1initially the wall of the bottle 1 comprised of synthetic material issaturated with CO₂ before CO₂ enters the interspace 3. In the case of aPET bottle having a wall thickness of 0.25 mm, a weight of 28 g, avolume of 0.5 l and the test gas CO₂, this saturation process takesapproximately 12 to 24 hours.

The pressure in the interspace therefore assumes the course depicted inFIG. 2, i.e. during a time t₂−t₁ it remains nearly constant, i.e. atvalue p_(Z)=p₀, and subsequently starting at t₂ increases nearlylinearly to the value p₃. If, before it is introduced into container 2,the bottle 1 is exposed for time t₂−t₁ to the internal pressure p_(F1),the horizontal section of the curve depicted in FIG. 2 is absent, andthe nearly linear curve rate of ascent, which is characterized in FIG. 2by the interval t₃−t₂, starts immediately. With the specified data of aPET bottle, the time segment t₃−t₂ is approximately 24 to 72 hours.

While the pressure in interspace 3 increases linearly or quasi-linearlyduring the time period t₃−t₂, the pressure in bottle 1 decreasescorrespondingly. As already explained above, the total leakage rate of atest sample, here of bottle 1, is q_(L)=V·Δp₁/Δt. This definition of thetotal leakage rate refers to the internal pressure of a test sample,with the external pressure being constant and, for example, is alwaysatmospheric pressure which is due to the fact that no container 2 isprovided.

In the configuration according to FIG. 1 such conditions do not obtain,since the pressure in interspace 3 increases continuously. Thepermeation through bottle 1 ends if the pressure in bottle 1 is equal tothe pressure in interspace 3, thus the conditionp_(F1)−Δp_(F1)=p_(Z)+Δp_(Z) obtains. Consequently, at the end of thepermeation no atmospheric pressure develops in bottle 1, as would be thecase in the absence of container 2.

In bottle 1, which according to assumption is only filled with CO₂ nopartial pressures are present. In contrast, the total pressure ininterspace 3 is only comprised of partial pressures, which are caused bythe different gas components in interspace 3 (Dalton's law). For thepresent invention, however, only the total pressures are of importance.In contrast to the known ascertainment of the total leakage rate, inwhich the pressure changes in bottle 1 are ascertained, according to theinvention the pressure course in interspace 3 is ascertained. Comparedto the measurement of the pressure course in bottle 1, measurement ofthe pressure course in interspace 3 has the advantage that themeasurements can be carried out at a low pressure level, for example1000 mbar, instead of 4000 to 6000 mbar, and thus a pressure sensor canbe applied with a smaller measuring range, for example 0 to 1500 mbar,which, at given resolution, for example 0.25% of the full-scaledeflection, supplies a markedly higher resolution than, for example, apressure sensor for the pressure range from, for example, 0 to 7500mbar. As pressure measuring instruments are herein possible for examplesuch, in which a mechanical or piezoelectric diaphragm, due to thepressure acting onto one of its sides, causes the deflection of thediaphragm, which represents a measure of the pressure.

As a measure for the permeation P the quantity$P = {V_{3} \cdot \frac{p_{3} - p_{2}}{t_{3} - t_{2}}}$

can be drawn on, where p₃ is the pressure in interspace 3 at time t₃ andp₂ the pressure in the interspace at time t₂.

The time period t₂−t₁, i.e. the time required until test gas CO₂penetrates through the bottle wall, as already stated, for a syntheticmaterial bottle comprised of PET, is approximately 12 to 24 hours, whiletime t₃−t₂ from the pressure rate of ascent in the interspace 3 to thestate p₃ for the same material is 24 to 72 hours.

If the volume of interspace 3 is large in comparison to the volume ofbottle 1, it requires a relatively long time until the pressure in theinterspace increases, since a large volume is fed through the permeationfrom a small volume. It is therefore advantageous to keep the interspace3 as small as possible relative to the volume of bottle 1. For thispurpose volume displacers can be introduced into interspace 3. It isalso possible to provide the inner wall of the container with ribbingson which the outer wall of bottle 1 abuts. Hereby it is simultaneouslyprevented that bottle 1 under excess pressure bulges out or bursts.

The permeation P defined here refers to the interspace 3. But itcorrelates with the total leakage rate q_(L) known from the literature,as becomes evident based on the following consideration: Since for idealgases in all pressure and temperature ranges the quotient pV/T isconstant, for the content of bottle 1 applies p_(F1)(t)·V_(F1)/T=K₁ andfor the content of the interspace p_(Z)(t)·V_(Z)/T=K₂. Thus, while thepressure in bottle 1 and in interspace 3 is a function of time, thevolumes of bottle 1 and interspace 3 remain constant. Consequently, atidentical temperature applies:$\frac{{p_{F1}(t)} \cdot V_{F1} \cdot T}{T \cdot {p_{z}(t)} \cdot V_{z}} = {\frac{K_{1}}{K_{2}} = K_{3}}$

The ratio of V_(F1) to V_(Z) is also a constant, such that$\frac{p_{F1}(t)}{p_{z}(t)} = {K_{4}\quad{applies}}$

orp _(F1)(t)=p _(Z)(t)·K ₄,

i.e. the pressure in the bottle and the pressure in the interspace arelinearly related—at least in the case of ideal gases and neglecting wallsaturation phenomena. This means that the permeation is proportional tothe total leakage rate q_(L).

If the course of the wall saturation with gas, as is characterizedprincipally by the time span t₂−t₁, is to be acquired more closely, itis also possible to set a pressure measuring instrument into the bottleitself. This pressure measuring instrument would be utilized, on the onehand, for controlling the filling process and determining the fillingpressure, while, on the other hand, it would measure the pressure coursein the bottle itself corresponding to the time spans t₂−t₁ and t₃−t₂ ofFIG. 2. As measurements show, this pressure course is not aquasi-straight curve as is the curve segment t₂−t₁ and t₃−t₂ in FIG. 2,but rather a curvilinear curve, in which a marked transition as at pointt₂ of FIG. 2 is not present. This circumstance contributes to the factthat a measuring of the internal pressure of the bottle permits lessprecise statements about the permeation proper of a bottle. Theemisssion of the gas, which is relatively sudden from the aspect of theinterspace, after the bottle wall has been loaded up with gas, has nocorrespondence from the aspect of the interior bottle measurements,since the mass flows are different. If, however, the saturation statehas been reached, the mass flows inside and outside of the bottle are ofequal magnitude. The behavior of a synthetic material until saturationis in many cases of significance. Thus, it is important to know whichgas quantity is necessary for saturation of the bottle wall or of theentire container at set pressure relations and set temperature.

In FIG. 3 a portion of an installation is depicted, with which thepermeations of several bottles or other containers can be determined. 20denotes a cover hood, which is slipped over overall four housings, ofwhich only two housings 21, 22 are evident in FIG. 3. In this housing21, 22 one bottle 23, 24 each is disposed, of which the bottle 23 has acontent of for example 1000 ml and the bottle 24 for example 500 ml.Into each of these bottles 23, 24 projects one flushing tube 25, 26 fortest gas, for example carbon dioxide, connected with a gas inlet line27, 28. Between the gas inlet lines 27, 28 and the flushing tubes 25, 26is provided a heating plate 29, into which the ends of pressure sensors30, 31 are set. The pressure sensors are preferably so-called absolutepressure sensors with preferably internally disposed diaphragms which atan ambient pressure of approximately 1000 mbar indicate the pressure tobe measured. Such absolute pressure sensors comprise an encapsulatedreference volume, such that external air pressure fluctuations duringthe measurement cannot exert any effect onto the measured pressurevalues. Air pressure changes before the start of the measurement changeonly the starting value of the measurement, which is withoutsignificance for the calculation of the slope of the pressure over time.Pressure sensors which are suitable for the described purposes, are forexample available on the market as piezoresistive or thin-film sensors(cf. IMT-Sensor 3248 by IMT Industrie-Meβtechnik GmbH, 60439 Frankfurt).Instead of absolute pressure sensors, sensors with negative or positiveexcess pressure can also be employed. Above these pressure sensors 30,31 are disposed threaded sockets 32, 33, into which threads 34, 35 ofbottles 23, 24 are screwed. The gas supplied to the bottles 23, 24 viathe flushing tubes 25, 26 can be controlled via valves 36, 37. Fromthese valves 36, 37 connection lines (not shown) lead to gas bottles,which are accommodated in a cabinet, which will be represented later, oroutside of this cabinet. Via these valves 36, 37 the gas flow to the gasinlet lines 27, 28 is controlled. The cover hood 20 can be raised orplaced on with the aid of handles 38, 39. 40 denotes a mounting for aresistance thermometer, with which the temperature in the container 21is measured. This temperature serves for regulating a heater realized bya heating plate 41. This heating plate is disposed beneath a base plate29. To avoid local hot spots, a ventilator 42 is provided whichcirculates the air within the cover hood.

FIG. 4 depicts a configuration of three housings 50, 51, 52, each ofwhich encompass a synthetic material bottle, not visible, as well as asynthetic material bottle 53 without housing. With this configuration itis possible to ascertain the permeation of four synthetic materialbottles simultaneously. The housings 50 to 52 and bottle 53 are locatedwithin a frame 54, which serves for receiving a cover hood. In front ofthis frame are disposed four stop cocks 55 to 58 as well as two fillingvalve switches 59, 60. The stop cocks 55 to 58 only have the task ofhermetically regulating off the interior bottle volume, as otherwise forexample cap 5 in FIG. 1. The filling valve switches 59, 60, in contrast,are control valves, with which the operating person by pressure ontoswitches 59, 60 can fill or empty the bottles. It is understood thatherein the stop cocks 55 to 58 must be open. The operating personconsequently has the option of filling single or several bottlessimultaneously. With the simultaneous filling of several bottles, whichis the rule, an exactly equal internal pressure can be attained in allbottles.

Housings 50 to 52 comprise at their lower end an annular plate 61 to 63,with which they can be fastened within the frame 54.

FIG. 5 shows in detail the securement. In the left representation ofFIG. 5 a housing 50 is shown with its annular plate 61 in a positionbefore the securement with a base 66. In plate 61 are provided threebores 67, 68, 69, each of which has a narrowing. To these bores 67, 68,69 correspond pins 70, 71, which comprise a shaft 72, 73 and a head 74,75 on the base 66. In order to secure the housing 50 on base 66, bores67, 68, 69 are slipped over the corresponding pins 70, 71. Subsequentlythe housing 50 is rotated relative to pins 70, 71 such that shafts 72,73 move into the narrowings of bores 67 to 69. Since the heads 74, 75 ofpins 70, 71 are wider than these narrowings, the housing sits firmly onthe base. The representation on the right side of FIG. 5 shows thehousing 50 in the arrested position.

FIG. 6 shows in its center a configuration as FIG. 4. To the right andleft of this configuration is disposed in each instance a hood 80, 81with two handles 82, 83 or 84, 85 each. Beneath each of these hoods 80,81 are located four measuring configurations with containers andbottles. Hoods 80, 81 with the measuring configurations are disposed ona cabinet 90 depicted only partially.

In FIG. 7 this cabinet 90 is shown completely. It comprises two doors91, 92, a latching 93 and four legs, of which only three legs 94, 95, 96are evident in FIG. 7.

The housings 50 to 52 or the bottle 53 depicted in FIG. 6 are notevident in FIG. 7 since a hood 100 with two handles 101, 102 is slippedover them. In front of the hood 80, 81, 100 are disposed in eachinstance four gas valve switches 103 to 106, 107 to 110 and 111 to 114.

Next to the cabinet is disposed a monitor 115 with a computer 116, whichis supported by a vertical arm 117, which, in turn, is swivellable abouta rotational axis of a horizontal arm 118. This horizontal arm 118 canbe connected with the cabinet 90.

Permeation determination with the aid of the device depicted in FIG. 3and 7 takes place such that with the hood 20 removed and the housing 21,22 removed, first the bottles 23, 24 with their open end are slid overthe flushing tubes 25, 26 and screwed into the threaded screw sockets32, 33. The containers 21, 22 are subsequently slipped over bottles 23,24 and sealed hermetically at their open ends. Hereupon by pressure ontobuttons 59, 60 and via gas inlet lines 27, 28 gas is introduced intobottles 23, 24 until a set pressure is developed. This pressure ismarkedly higher than the pressure obtaining between a container 21, 22and a bottle 23, 24. Although the bottles 23, 24 are filled exclusivelywith a gas, it should be pointed out that the invention is alsoapplicable with bottles or other containers, which are filled with agas-containing liquid.

The pressure obtaining between a container 21, 22 and a bottle 23, 24 ispreferably atmospheric pressure. However, a different pressure can alsobe set. After the preset pressure has been reached in the bottles 23,24, the gas inlet lines 27, 28 are closed by means of the stop cocks 55to 58. After a constant temperature in housing 20 and containers 21, 22has been reached, the initial pressure p₀ in the interspace 3 measuredby means of the pressure sensors 30, 31, remains nearly constant up to atime t₂ and subsequently increases relatively steeply. This rate ofascent can be acquired for example thereby that the pressure is measuredat specific short time intervals and compared with the particularpressure measured previously. During the time period t₂−t₁ the pressuredifference determined thereby is very small. However, after time t₂ thispressure difference increases steeply. If previously a specific pressuredifference has been defined as a threshold value, and if this thresholdvalue is exceeded, reaching the break point at site t₂ can automaticallybe ascertained. The pressure differences occurring within set timeperiods, are subsequently measured.

These pressure differences are divided by the time interval within whichthey have developed, and the resulting quotient is multiplied by thevolume of the interspace 3. The obtained value represents the permeationrate.

In the case of expandable bottles and at very high pressures in thesebottles, the measurement of the absolute permeation rate is slightlyfalsified thereby that the volumes in the bottle and in the interspacebetween container and bottle are not constant. Rather, the volume of thebottle increases with increasing pressure while the volume in theinterspace decreases. However, it is possible to ascertain the ratios ofthe volumes as a function of the particular pressures in calibrationmeasurements and to take them into account with the values measuredlater.

In the principal application of the invention, namely the ascertainmentof a permeation decrease with the coating of the bottle, the abovedescribed error however, does not manifest itself since it is canceledout. The improvement factor of permeation P, attained through a coating,is defined by the quotient:$K_{v} = \frac{P_{{without}\quad{coating}}}{P_{{with}\quad{coating}}}$

Since herein applies$K_{v} = \frac{V_{3}\frac{\Delta\quad p_{{without}\quad{coating}}}{\Delta\quad t_{{without}\quad{coating}}}}{V_{3}\frac{\Delta\quad p_{{with}\quad{coating}}}{\Delta\quad t_{{with}\quad{coating}}}}$applies, the variable V₃ is canceled out and for the improvement processnow only$K_{v} = \frac{\Delta\quad{p_{{without}\quad{coating}} \cdot \Delta}\quad t_{{with}\quad{coating}}}{\Delta\quad{t_{{without}\quad{coating}} \cdot \Delta}\quad p_{{with}\quad{coating}}}$

remains.

Since the measuring intervals before and after coating were the same, orshould have been the same, in order to be able to detect the actualimprovement, the times are also canceled out such that for theimprovement only the pressure ratio is critical:$K_{v} = {\frac{\Delta\quad p_{{without}\quad{coating}}}{\Delta\quad p_{{with}\quad{coating}}}.}$

In the above described example the bottle was filled with CO₂ only afterit had assumed the position depicted in FIG. 3. Hereby the course shownin FIG. 2 is generated.

It is, however, also possible to provide the bottle previously with anexcess pressure and to allow it to rest in the closed state until thesaturation of the bottle walls with the excess pressure gas iscompleted. If these two bottles already filled with excess pressure gasare now placed into the device according to FIG. 3 and if the container21, 22 is slipped over it, in this case in the interspace 3 a pressurerate of ascent sets in immediately such as is depicted in FIG. 2 for thetime span t₃−t₂. The further procedure can subsequently proceed in thesame manner as in the procedure in which the bottles are only filledwith gas after emplacement in the measuring device.

If for specific reasons it is not possible to keep the interspacebetween a bottle and the container encompassing it smaller than thecontent of the bottle, the invention can also be realized through akinematic reversal. Herein the volume of the bottle would be smallerthan the volume of the interspace, the pressure in the interspace wouldbe higher than that in the bottle and the pressure measurements would becarried out in the bottle.

Since it is especially important to ascertain the gas permeability of acontainer rapidly, it is especially advantageous to utilize a gas with ahigher permeation rate as the test gas instead of the gas for which abarrier protection effect is desired. If, for example, instead of CO₂,helium is utilized as the test gas, in the case of PET bottles measuringtimes of only a few hours result instead of, for example, 2 to 4 days.Since the correlation between the permeation of the test gas and thepermeation of the gas to be used subsequently in the bottles or thecontainers is know or can be detected experimentally, it is possible toconvert subsequently the numerical values ascertained with the gas ofhigh permeation.

It is understood, that with the aid of software negative effects causedby strong temperature variations and saturation effects, are alsoautomatically eliminated.

In a preferred embodiment, a device for the determination of the gaspermeability of a container (1; 23, 24) with the volume V₁, has anenclosure (2; 21, 22) for the container (1; 23, 24). The enclosure (2;21, 22) has a volume V₂. The device has a pressure measuring apparatuswhich measures the gas pressure in the container (1; 23, 24); a devicefor generating excess pressure in the space (3) between enclosure (2;21, 22) and container (1; 23, 24) in comparison to the pressure in thecontainer (1; 23, 24); a volume ratio far the volumes of container (1;23, 24) and enclosure (2; 21, 22) for which the relation V₂−V₁>V₁applying; and an apparatus which ascertains the gas permeability of thecontainer (1; 23, 24) from the time course of the measured pressure.

1. A device for the determination of the gas permeability of asubstantially rigid hollow body with the volume V₁, comprising: asubstantially rigid container enclosing said hollow body, said containerhaving the volume V₂ and a distance from said hollow body; a pressuremeasuring instrument which measures the gas pressure in the spacebetween the container and the hollow body; an apparatus which ascertainsthe gas permeability of the hollow body from the time course of themeasured pressure; gas supplying means for the generation of excesspressure in said hollow body in comparison to the pressure in the spacebetween the hollow body and the container, whereby the pressure in saidspace between said hollow body and said container corresponds toatmospheric pressure at the beginning of the determination of the gaspermeability; and a volume ratio for the volumes of the hollow body andthe container for which the relationV ₂ −V ₁ <V ₁ applies.
 2. A device for the determination of the gaspermeability of a substantially rigid hallow body with the volume V₁,comprising: a substantially rigid container enclosing said hollow body,said container having the volume V₂ and a distance from said hollowbody; an apparatus which ascertains the gas permeability of the hollowbody from the time course of the measured pressure; a pressure measuringapparatus which measures the gas pressure in said hollow body; gassupplying means for generating excess pressure in the space between saidhollow body and said container in comparison to the pressure in thehollow body; and a volume ratio for the volumes of said hollow body andsaid container for which the relationV ₂ −V ₁ <V ₁ applies.
 3. The device as claimed in claim 1, wherein thepressure measuring element is disposed at any desired site between thecontainer and the enclosure.
 4. The device as claimed in claim 1,wherein the pressure measuring clement is disposed outside of theenclosure and is connected via a channel with the interior volume of theenclosure.
 5. The device as claimed in claim 1, wherein the volumebetween the inner wall of the enclosure and the outer wall of thecontainer is as small as possible without hindering the emission of gasfrom the container.
 6. The device as claimed in claim 1, wherein aheater to maintain the temperatures of the gas in the container and ofthe gas in the interspace between container and enclosure constant at aset temperature.
 7. A device for the determination of the gaspenetrability of a container with the volume V₁, comprising: anenclosure for the container with the enclosure having the volume V₂; apressure measuring instrument which measures the gas pressure in thespace between the enclosure and the container; gas supplying means forthe generation of excess pressure in the container in comparison to thepressure in the space between the enclosure and the container; a volumeratio for the volumes of container and enclosure, for which the relationV ₂ −V ₁ <V ₁ applies; and an apparatus which ascertains the gaspermeability of the container from the time course of the measuredpressure; wherein a body provided with an inner threading is provided,into which the outer threads of a container can be screwed.
 8. Thedevice as claimed in claim 1, wherein several devices for thedetermination of the gas permeability of a container are combined intoone unit, which are covered with a hood.
 9. The device as claimed inclaim 8, wherein several units covered by a hood are disposed on acommon cabinet.
 10. The device as claimed in claim 9, further comprisinga monitor with a computer.
 11. The device as claimed in claim 1, furthercomprising a pressure measuring element is additionally disposed in thecontainer.
 12. A method for determining the gas permeability of acontainer comprising the steps of: encompassing the container with anenclosure to hermetically seal the container; bringing the space betweenthe enclosure and the container to a set pressure; wherein the pressurein the container is brought by means of a test gas above the pressure inthe enclosure; measuring the pressure in the interspace between theenclosure and the container over a set time period continuously or atspecific time intervals; and detecting a value that exceeds a setthreshold value of the pressure above the atmospheric pressure andstoring the ascertained pressure value p₂ and time t₂ at which thepressure value p₂ occurs; ascertaining a pressure value p₃ after a settime t₃−t₂ and the permeation$P = {{V_{3} \cdot \frac{p_{3} - p_{2}}{t_{3} - t_{2}}} = {V_{3} \cdot \frac{\Delta\quad p}{\Delta\quad t}}}$ is calculated.
 13. A method for the determination of the gaspermeability of a container comprising the steps of: exposing thecontainer below a gas pressure which is above the pressure on theoutside of the container; exposing the container for a set time to thepressure on its outside, with this time corresponding approximately tothat time which must pass for the wall of the container to be saturatedwith the gas which is in the container; encompassing the container afterthe set time in an enclosure to hermetically encompass the container;bringing the space between enclosure end container to a set pressure;measuring the pressure in the interspace between enclosure and containerover a set time period continuously or at specific time intervals;detecting the exceeding of a set threshold value of the pressure abovethe atmospheric pressure and storing pressure value p₂ as well as thetime t₂ at which the pressure value p₂ occurs: and a pressure value p₃after a set time t₃−t₂ is ascertained and the permeation$P = {{V_{3} \cdot \frac{p_{3} - p_{2}}{t_{3} - t_{2}}} = {V_{3} \cdot \frac{\Delta\quad p}{\Delta\quad t}}}$ is calculated.
 14. A method as claimed in claim 12, wherein the setpressure in the space between enclosure and container at the beginningof the method is equal to the pressure of the ambient atmosphere.
 15. Amethod as claimed in claim 13, wherein the set pressure in the spacebetween enclosure and container at the beginning of the method is equalto the pressure of the ambient atmosphere.
 16. A method as claimed inclaim 14, wherein the pressure in the interspace between enclosure andcontainer is measured by means of an absolute pressure measuringinstrument.
 17. A method as claimed in claim 13, wherein the pressure inthe interspace between enclosure and container is measured by means ofan absolute pressure measuring instrument.